1. Field of the Invention
This invention relates to bonding of electronic devices as particularly applied to the building of stacks of layers of electronic devices, e.g., IC chips, which are stacked and bonded together to provide a high-density electronic package.
2. Brief Statement of the Prior Art
Heretofore, the generally used chip stacking process has been similar to that disclosed in U.S. Pat. No. 4,617,160 which discloses a "wet stacking" process. In this process, a measured amount of adhesive, generally an epoxy adhesive, is applied to each chip as the stack is laminated. After the last chip has been positioned on top of the stack, a force is applied to the stack which forces excess epoxy to extrude from the stack, followed by the application of heat to effect "curing" of the epoxy. The adhesive thickness, after curing, is in the order of 1 to 3 micrometers. While desirable results are obtained with this technique, it is time consuming and labor intensive, and results in a considerable amount of adhesive on the faces of the stack which has to be removed.